A pocket calculator is a battery-powered electronic device used to perform simple arithmetic calculations upon data input. Pocket calculators got their name owing to their compact size, which is sufficiently small and handy, and can be carried in a pocket.
The Busicom LE-120A HANDY was the first real pocket-sized calculator, which was made in Japan and was marketed during early 1971.
Techopedia explains Pocket Calculator
Originally, all calculators were mechanical calculators. Electronic calculators were introduced in the early 1960s, which were quite large in size due to the use of several transistors, a huge power supply and other bulky parts. Then, in early 1970s pocket calculators were developed.
A typical pocket calculator consists of the following:
Input keypad: A keypad consisting of plastic keys, a rubber membrane as well as a touch-sensitive circuit below it
Processor: The microchip that does all the computations
Output screen: A liquid crystal display (LCD) to show the keyed-in digits and calculated output
Power source: A long-life battery, now mostly small button batteries. Some calculators feature a solar cell to offer free power during daylight as well.
As technology advanced, variants of pocket calculators, such as pocket computers and graphing calculators, have been introduced. Pocket calculators are now facing extinction, a victim of digitization. With the advancement of computers and mobile technology, pocket calculators have transformed and are mostly found in the form of a feature on mobile phones and desktops rather than as a standalone gadget.